Emissions from a diesel engine, gasoline engine, natural gas engine, and other engines known in the art, may include particulate matter and other pollutants carried with engine exhaust. Exhaust aftertreatment systems generally include a diesel particulate filter, a diesel oxidation catalyst, and a selective catalytic reduction catalyst placed in the engine exhaust to reduce the amount of pollutants released into the atmosphere. The exhaust aftertreatment systems may separate or convert the pollutants to less noxious compounds.
A diesel particulate filter may collect particulate matter and remove it from the exhaust. However, over time, particulate matter may build-up and clog the filter, thereby impairing filter performance. Filter regeneration methods are designed to remove the built-up particulate matter from the filter, and improve filtration capacity/characteristics of the filter. An active regeneration method includes burning the accumulated particulate matter at elevated temperatures to thereby increase the filtration capacity of the filter. During the regeneration process, a fuel and air mixture is typically injected into a flame chamber upstream of the filter. The mixture is then ignited with a flame to burn the particulate matter captured by the downstream filter.
U.S. Pat. No. 7,406,822 issued to Funke et al. on Aug. 5, 2008 (the '822 patent), describes an exemplary system and method for active filter regeneration. In particular, a flame sensing system of the '822 patent uses thermocouples to detect whether a flame is present upstream of a particulate filter, and to monitor the amount of fuel required to maintain a sufficient flame. When no flame is present, the system may terminate the injection of fuel. However, when a flame is present, the amount of fuel may be adequate and the system may monitor the presence of fuel.
While the system disclosed in the '882 patent may be capable of detecting the presence of a flame, such systems are typically plagued with several disadvantages. For example, although thermocouples may be configured to detect the presence of a flame, thermocouples typically have a slower response time than other sensors. As a result, systems injecting fuel based on signals received from such thermocouples may continue to inadvertently inject fuel into the flame chamber while a flame is no longer present. Such excess fuel may flow downstream into the filter, and may crack or melt the filter causing permanent damage to the filter. Additionally, thermocouple sensors may be required to be located directly in the flame. The extreme temperatures of the flame may decay the thermocouple so that it may no longer work properly.
The disclosed system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.